The carbon dioxide system on the Mississippi River‐dominated continental shelf in the northern Gulf of Mexico: 1. Distribution and air‐sea CO2 flux. Issue 3 (3rd March 2015)

• Record Type: Journal Article
• Authors: Huang, Wei‐Jen; Cai, Wei‐Jun; Wang, Yongchen; Lohrenz, Steven E.; Murrell, Michael C.
• Is Part Of: Journal of geophysical research. Volume 120:Issue 3(2015:Mar.)
• Page Start: 1429
• Page End: 1445
• Publication Date: 2015-03-03
• Subjects: Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2014JC010498
• Languages: English
• ISSNs: 2169-9275

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>River‐dominated continental shelf environments are active sites of air‐sea CO<sub>2</sub> exchange. We conducted 13 cruises in the northern Gulf of Mexico, a region strongly influenced by fresh water and nutrients delivered from the Mississippi and Atchafalaya River system. The sea surface partial pressure of carbon dioxide (<italic>p</italic>CO<sub>2</sub>) was measured, and the air‐sea CO<sub>2</sub> flux was calculated. Results show that CO<sub>2</sub> exchange exhibited a distinct seasonality: the study area was a net sink of atmospheric CO<sub>2</sub> during spring and early summer, and it was neutral or a weak source of CO<sub>2</sub> to the atmosphere during midsummer, fall, and winter. Along the salinity gradient, across the shelf, the sea surface shifted from a source of CO<sub>2</sub> in low‐salinity zones (0≤S<17) to a strong CO<sub>2</sub> sink in the middle‐to‐high‐salinity zones (17≤S<33), and finally was a near‐neutral state in the high‐salinity areas (33≤S<35) and in the open gulf (S≥35). High <italic>p</italic>CO<sub>2</sub> values were only observed in narrow regions near freshwater sources, and the distribution of undersaturated <italic>p</italic>CO<sub>2</sub> generally reflected the influence of freshwater inputs along the shelf. Systematic analyses of <italic>p</italic>CO<sub>2</sub> variation demonstrated the importance of riverine nitrogen export; that is, riverine nitrogen‐enhanced biological removal, along with mixing processes, dominated <italic>p</italic>CO<sub>2</sub> variation along the salinity gradient. In addition, extreme or unusual weather events were observed to alter the alongshore <italic>p</italic>CO<sub>2</sub> distribution and to affect regional air‐sea CO<sub>2</sub> flux estimates. Overall, the study region acted as a net CO<sub>2</sub> sink of 0.96 ± 3.7 mol m<sup>−2</sup> yr<sup>−1</sup> (1.15 ± 4.4 Tg C yr<sup>−1</sup>).</p> </abstract>